Safety ski bindings of the foregoing type are, for instance, described in German Patent 3,307,003 A1 in which when the ski boot is not inserted into the binding, a choke included therewith is positioned in a mode in which its cross-section is at a maximum. When the ski boot is placed in the binding, however, the electronic circuitry is activated and a blocking member, actuated by an electromagnet, causes a reduction of the choke's cross-section. In its latter condition, the cross-section constitutes a reference control value.
The release spring of such a binding is designed so that it opposes the release forces acting on the sole holder of the binding with the minimum resistance required for skiing, the cross-sections of the ducts associated with the bindings being suitably dimensioned to ensure the attainment of a small shock-absorbing effect independent of the choke. Additional forces transmitted by the ski boot to the sole holder or to the ski, that is forces which do not directly act on the sole holder with a releasing effect, are detected by sensors and lead to an increase in the passage cross-section, and thus to a reduction of the choke's resistance to the flow of hydraulic fluid therethrough. In this way there is a regulation or automatic control of the overall resistance to binding release which is dependent on the loads being experienced by the bindings.
If as a consequence of some failure, the electromagnet is not supplied with the appropriate electric current, a return spring presses the blocking member back so that the maximum passage cross-section is reset to a value greater than the reference control value. This condition is even more hazardous for well-trained, expert skiers, however, since unintended releases may result, with the consequence that non-typical accidents and resultant injuries can occur to the skier.
If on the contrary there is a malfunction of the electronic circuitry such that there is no necessary decrease in current to the electromagnet to accommodate a load, no desired reduction of the damping resistance of the choke occurs, and the skier may experience an overloading of his or her leg and thus suffer a typical skiing injury.
With reference to the general state of the art concerning safety ski bindings with hydraulic components, reference may also be had to the Austrian Patent 373,159 as one of a series of publications.